Which VW diesels can be fixed (updated), and which can't?

More than 16 months after Volkswagen's use of illegal "defeat device" software in diesel vehicles was announced by the Environmental Protection Agency, some progress is finally being made in addressing the affected cars.

Settlements are now in place for almost half a million VW and Audi models with 2.0-liter TDI 4-cylinder engines, as well as roughly 80,000 VW. Audi, and Porsche vehicles equipped with 3.0-liter TDI V-6 engines.

But so far, only a relatively small number of these vehicles can be modified to meet emissions standards and stay on the road.